<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

</body>
<script>
    var damu = {damu:"达姆"}

    function foo() {}
    foo.prototype = {a:"a"}
    foo.prototype.__proto__ = damu

    var f1 = new foo()
    console.log(f1.damu)
    
    
</script>
</html>